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Installation of a generator for a house.

Tomgunn
Hello all,


I'm moving house, (been here for over 42 years'!!), and one of the first items on my mind is installing an electrical generator.


SO; I guess there will be contactors / switch gear etc as I would like it to be 'automatic', (OR, maybe 'manual' too), changing from incoming to the generator.


a; What would be the best type of generator to purchase? Load wise? I'm not too worried as the bigger the load the bigger the           generator would need to be as long as I could run the basics within the house.


b; What switch gear would be appropriate?


I would't fancy the idea of switching tails around on a Henley block each time I needed the generator to be in use!!


Thanks, in advance!


regards... Tom
  • 0
    I would, if possible, avoid an RCD on the mains supply from house to generator hut. Too much risk of nuisance tripping. Do of course fit RCDs as required at the load end.

    I would not fit an RCD to the generator output, again for risk of nuisance tripping. At the generator hut, connect together all the following

    Outgoing neutral.

    Outgoing earth.

    Frame of machine.

    Local earth rod.

    Any structural metalwork or other services.

    The armouring of all the SWA cables.

    The bare copper earth tape that you buried with the cables.

    The generator supply will then resemble a small public supply of type TN-S.

    Add RCDs as desired at the load/house end.


    Most "proper" diesel generators come with an engine block heater or oil sump heater. Control via a thermostat to avoid waste in mild weather.


  • 0
    I would not fit an RCD to the generator output, again for risk of nuisance tripping.

    But do be aware that the available current from a genset is much lower than from the mains, and you need to check breaker ratings and PSSC to see - you may find you need an RCD (though not perhaps a 30mA instant one) to ensure that you have some sort of  certainty that ADS will work when on genset if it looks like breakers and fuses won't operate, but the volts collapse instead. The output impedance of a generator, and so the Zs and PSSC, is a function of the current throttle setting, and in turn varies with the load. It is quite possible to stall a lightly loaded generator without operating any MCBs or fuses. (on at least one model it is also possible to shear a pin in the drive train by applying a short circuit when near full load one,  when the throttle is at max to maintain the revs, but that is another embarrassing story.)

    Unless you have some nasty loads in the house, it should be possible to arrange things so there should not be false tripping of a delay type RCD if you decide you need one.
  • 0
    broadgage:

    I would, if possible, avoid an RCD on the mains supply from house to generator hut. Too much risk of nuisance tripping. Do of course fit RCDs as required at the load end.

    I would not fit an RCD to the generator output, again for risk of nuisance tripping. At the generator hut, connect together all the following

    Outgoing neutral.

    Outgoing earth.

    Frame of machine.

    Local earth rod.

    Any structural metalwork or other services.

    The armouring of all the SWA cables.

    The bare copper earth tape that you buried with the cables.

    The generator supply will then resemble a small public supply of type TN-S.

    Add RCDs as desired at the load/house end.


    Most "proper" diesel generators come with an engine block heater or oil sump heater. Control via a thermostat to avoid waste in mild weather.


     


    Well, more great info, no really! ?


    I didn't know that generators come with a heating unit fitted?


    Bond up everything, then???


    Lucky I have 'bookmarked' this thread... wow!


    Thanks again!!


    All the best, to everyone, for 2021.


    regards... Tom


  • 0
    mapj1:
    I would not fit an RCD to the generator output, again for risk of nuisance tripping.

    But do be aware that the available current from a genset is much lower than from the mains, and you need to check breaker ratings and PSSC to see - you may find you need an RCD (though not perhaps a 30mA instant one) to ensure that you have some sort of  certainty that ADS will work when on genset if it looks like breakers and fuses won't operate, but the volts collapse instead. The output impedance of a generator, and so the Zs and PSSC, is a function of the current throttle setting, and in turn varies with the load. It is quite possible to stall a lightly loaded generator without operating any MCBs or fuses. (on at least one model it is also possible to shear a pin in the drive train by applying a short circuit when near full load one,  when the throttle is at max to maintain the revs, but that is another embarrassing story.)

    Unless you have some nasty loads in the house, it should be possible to arrange things so there should not be false tripping of a delay type RCD if you decide you need one.


    Thanks mapj1...


    I need to re-read this a few times... as per usual you have some amazing information and thanks!


    Regards... Tom


  • 0
    Whilst I see one or two useful points, small generators do not need or have sump heaters, nor does your diesel car, which I assume will start tomorrow. Very large machines may, even here but the reason is not freezing but that they are very hard to turn over with batteries at the best of times when cold. A 5MVA machine needs a ton of batteries of very high capacity and of course voltage. Usually, very large machines such as those on ships usually have air starting, or a smaller generator to provide the starting power. It is certainly unnecessary on a 5kVA type which everyone thinks would suit, although I think the same money on a 30 or 40 kVA silent one would be much better value and 100 times more useful and reliable.


    Going on to CPDs, a 5kVA machine would probably stall on a ring short before it popped a type B, and you will certainly have no circuit overload protection. You probably don't need it either working from a generator. You will need an RCD as Earth faults also will not trip the CPD, I suggest a 300mA delayed one at the generator. You can put what you like in the CU, The PSCC on a 5kVA generator is probably only 50 or 60A at the terminals. This is simply because the engine cannot give much power, and any flywheel will be very small. Stalling is the most likely outcome of any problem.
  • 0
     The output impedance of a generator, and so the Zs and PSSC, is a function of the current throttle setting, and in turn varies with the load. It is quite possible to stall a lightly loaded generator without operating any MCBs or fuses. 


    I'm interested in why a lightly loaded genny should have a lower PSSC.

    I would have thought that the instantaneous fault current depended on the inertia which doesn't change with load and the longer term fault current (more than 1 sec) would depend on how much spare capacity was left on the throttle so it would larger for low loads.

    Large UPS systems also have this problem and maybe the answer is to have an undervoltage relay that senses the fall in voltage from a larger fault.


  • 0


    As the revs are supposed to stay constant under load to maintain frequency, to put more power out  the current in the armature  rises and the fuel flow is increased, to match the higher torque - if you like a simple picture the rotating magnetic field has to  become stronger, and so the effort to turn it is greater. so is the stored energy.

    In some gensets this is explicit as there are brushes onto slip rings for the rotor, but for more common induction designs, the same effect is achieved by the sliding phase shift - rather like the not quite synchronous 3 phase induction motor but in reverse.

    The PSSC is low enough that to operate  that B32 breaker takes a what would be a good few cycles of 50Hz if it was not slowing down significantly during the breaker operating time, you will  probably not be in the magnetic instant trip part of the curve, so it is not just the flywheel and rotor inertia, but also a few good kicks of the pistons onto the crankshafts - and that is when the stall vs falter but keep going, or indeed snap the shear pin, all depends rather on the throttle setting...

    M.
  • 0
    mapj1:

    It is quite possible to stall a lightly loaded generator without operating any MCBs or fuses. (on at least one model it is also possible to shear a pin in the drive train by applying a short circuit when near full load one,  when the throttle is at max to maintain the revs, but that is another embarrassing story.)


    davezawadi (David Stone):

    Going on to CPDs, a 5kVA machine would probably stall on a ring short before it popped a type B ...

    Well, that shear pin was in there for a reason. ?


    It's a bit like letting the clutch out a bit swiftly at the bottom of Sutton Bank. ?


  • 0
    I suspect that the PSCC is irrelevant in the context of a 32A MCB as the genny will not be able to produce much more than  the rated current (8kW) so the wiring is protected by the generator output limit. A fault would still constitute a fire risk and shock risk but an RCBO should pick these up.

    More relevant may be whether a 6A MCB would trip.
  • 0
    davezawadi (David Stone):

    Whilst I see one or two useful points, small generators do not need or have sump heaters, nor does your diesel car, which I assume will start tomorrow. Very large machines may, even here but the reason is not freezing but that they are very hard to turn over with batteries at the best of times when cold. A 5MVA machine needs a ton of batteries of very high capacity and of course voltage. Usually, very large machines such as those on ships usually have air starting, or a smaller generator to provide the starting power. It is certainly unnecessary on a 5kVA type which everyone thinks would suit, although I think the same money on a 30 or 40 kVA silent one would be much better value and 100 times more useful and reliable.


    Going on to CPDs, a 5kVA machine would probably stall on a ring short before it popped a type B, and you will certainly have no circuit overload protection. You probably don't need it either working from a generator. You will need an RCD as Earth faults also will not trip the CPD, I suggest a 300mA delayed one at the generator. You can put what you like in the CU, The PSCC on a 5kVA generator is probably only 50 or 60A at the terminals. This is simply because the engine cannot give much power, and any flywheel will be very small. Stalling is the most likely outcome of any problem.


    Hello David...


    I'm certainly getting some great feedback, on here!


    You're probably right, re; the 30 or 40 kva... 


    It's interesting to read so many suggestions and I guess I'll aim for the middle of the road, approach?


    Thanks!

     


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